1. Field of the Invention
The invention concerns a radio-based system for identifying persons, animals or objects wearing or carrying identifying transponder type badges. It is also concerned with the component parts of a system of this kind, such as a badge interrogator and a receiver processing at least in part the responses provided by the badges, the badge itself and applications of a system of this kind.
2. Description of the Prior Art
The identification of persons, animals or objects by means of badges is conventionally applied directly in entry or transit control and indirectly in presence control.
Each badge has a characteristic that can be recognized by an appropriate identification system, either individually or within a category.
The recognition of the characteristic of a badge by an identifier system implies the use of an information receiver with which the badge is required to communicate.
This communication can be established at the initiative of the badge wearer in some applications, in particular when the wearer requires access. It can also be initiated automatically by the presence of the badge wearer without the latter having to do anything in particular, for example when initiation is triggered by the passage of the badge through an accessway equipped to achieve this.
It is standard practice in microwave communications and in particular in radio direction finding to trigger the transmitter of a transmitter-receiver device by sending a signal to the receiver of the device from an interrogator.
This method can be used with a transmitter-receiver implemented as a badge and relieves the badge wearer of any need to concern himself with setting up a communication link, so that badges can be assigned to "wearers" in whom no responsibility need be placed, such as animals and objects.
The badge must then either incorporate its own power source or receive external power enabling it to transmit to the receiver(s) of the radio identification system.
For technical and economic reasons that are well known in the field of radio communications, transmission by the interrogators and the badges is discontinuous and initiated only when necessary, insofar as this is possible.
One technical reason for minimizing transmission by the badges is that it entails the consumption of power from a supply whose state of depletion and/or deterioration must be checked periodically if the supply is incorporated into the badge.
This constraint is a major drawback in radio identification systems where the badge wearer is often required to assume minimal or even no responsibility with regard to the radio identification equipment.
A second technical reason for minimizing the duration of transmission by the badges is related to congestion and radio frequency interference that could be caused by long and/or simultaneous transmissions, to the detriment of both the radio identification system itself and the general environment.
The duration of transmissions by the badges and the possibility that more than one badge may transmit at a time have a direct influence on the identification capacity of the radio identification system, on the complexity of the identification receiver(s) and on the system in general.
The present invention is therefore concerned with a system for identifying persons, animals or objects provided for this purpose with transponder type identifying badges.
It also concerns the component parts of a system of this kind such as a badge interrogator and a receiver processing at least in part the responses provided by the badges and applications of a system of this kind.